Automatic volume control receiver



May 5 i936." c. WAV@ AUTOMATIC VOLUME CONTROL REOEIVER Filed Nov. 8, 1932 QS .SQ

Patented May 5, 1936 UNITED STATES PATENT OFFICE Charles Travis, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application November 8, 1932, Serial No. 641,711

14 Claims.

My present invention relates to radio receivers, and more particularly to a radio receiver of the type employing automatic volume control wherein the apparent tuning selectivity of the receiver is greatly increased.

It has been found in tuning radio receivers employing automatic Volume control that a certain degree of distortion results in determining the desired signal carrier setting on the tuning dial when only the ear of the said operator is relied upon. This distortion is best explained as resulting from an apparent diminution in reproducer volume at the tuning dial setting corresponding to the desired signal carrier, and a relative increase in reproducer volume on either side of the last mentioned dial setting. The tendency, therefore, exists to adjust the tuning dial of the receiver to a point on either side of the desired carrier setting in the mistaken belief that either of such points is the true signal carrier dial setting. This, of course, results in distortion because of cutting of modulation side bands.

It has, therefore, been proposed to employ a visual device, such as a tuning meter, at some point in the receiver which is responsive to the modulated signal carrier energy being detected. 'Ihe use of such a tuning meter provides a visual check on the ear of the operator with the result that the tuning dial may be adjusted to that setting at which a reading on the tuning meter corresponds to a predetermined signal carrier point, such a point usually being an intermediate point on the tuning meter scale. However, the employment of a tuning meter requires the introduction into the set of additional wiring, and requires a certain degree of attention on the part of the said operator which the average broadcast receiver user is not very willing to give.

Now, I have discovered a method of, and means fo-r, tuning a radio receiver employing automatic volume control, which method utilizes a coupling network prior to the automatic volume control device, possessing a resonance characteristic such that the ear of the said operator may be utilized for accurately determining when the tuning dial has been adjusted to the desired signal carrier setting, thereby eliminating the need for the use of any instrumentality, such as a visual tuning meter, other than the operators ear for accurately tuning a radio receiver of this type.

Accordingly, it may be stated that it is one of the main objects of my present invention to provide a radio receiver employing an automatic volume control circuit having its input coupled in such a manner to a radio frequency portion (Cl. Z50-20) of the receiver that the resonance curve of the input circuit of the volume control includes a double peak and a pronounced depression between the two peaks corresponding to a desired signal carrier frequency.

Another important object of the present invention is to provide a radio receiver of the type utilizing a frequency changer circuit for producing an intermediate frequency, an intermediate frequency amplifier, an automatic volume control tube, and an automatic volume control amplifier for amplifying a portion of the input to the intermediate frequency amplifier, the circuit of the automatic volume control tube and the output circuit of the automatic volume control amplifier being substantially overcoupled.

Another object of the present invention is to provide a superheterodyne receiver of the type employing a radio frequency amplifier, a first detector, a local oscillator, an intermediate frequency amplifier, and a second detector, wherein the input of the intermediate frequency amplifier is additionally connected to a network including an amplifier and an automatic volume control tube of the diode type, there being connections between the anode circuit of the volume control diode and the input circuits of the radio frequency amplifier and the intermediate frequency amplifier whereby the gain of the latter may be automatically controlled in response to variations of the signal carrier energy level, the coupling between said control network amplifier and control diode being such that the receiver operator may readily and accurately tune the receiver by ear to a desired signal carrier setting.

And still other objects of the present invention are to improve generally the simplicityand tuning efficiency of radio receivers utilizing automatic volume control, and to particularly provide such a receiver which is not only reliable in operation, but economically manufactured and assembled.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawing, Y

Fig. 1 diagrammatically shows a superheter- Fig. 3 graphically shows the operation of the' receiver of Fig'. 1,

Fig. 4 diagrammatically shows a modification of the invention, and

Fig. 5 shows still another modification.

Referring now to the accompanying drawing wherein like reference characters designate similar circuit elements in the different figures, the superheterodyne receiver conventionally shown in Fig. 1 comprises a, signal source I which may be the usual antenna circuit, a radio frequency distribution system, or any other well known type of broadcast signal collecting device. The source I is coupled, as at M1, to the tunable input circuit of a radio frequency amplifier 2, the input circuit including a variable tuning condenser 3. The output circuit of the amplifier 2 is coupled, as at M2, to the tunable input circuit of the first detector 4, a variable tuning condenser 5 being connected in the input circuit of the latter.

A local oscillator 6 is shown in generalized form as being arranged for coupling tothe first detector circuit so that the locally generated oscillations may be impressed upon the first detector, or frequency changer, to produce the desired intermediate frequency in the output circuit of the first detector. The local oscillator 6 includes a tuned circuit having the tuning condenser 'I therein, and any well known type of mechanical uni-control 8, shown in dotted lines, may be employed for simultaneously adjusting the tuning condensers 3,y 5 and 1.

Reference is had to U. S., Patent 1,740,331 to W.,L. Carlsonl issued; December 17, 1929 to show a preferred methodV of,y arranging the tunable circuits of the amplifier 2, first detector 4, and local oscillator 6 in order toY produce in the output circuit ofthe detector 4 a constant desired intermediate frequency'while simultaneously adjusting the tuning: condensers 3, 5 and I. The output circuit of; the first detector 4 is coupled, as at M3, to the input circuit of the intermediate frequencyrarnplier 9, andtheinput circuit of theY second detector Il?v is coupled to the output` circuit of the amplifier 9 through a coupling transformer M4.

The coupled circuits betweenthe first detector 4.

and theV amplifier 9 as well. as'. between the .am-

. plifier Y9 and thesecond detector ID, are all maintained fixedly tuned to the intermediate frequency, whichmay` be kilocycles. 'I'he transformers M3 and M4. are preferably both tuned Vto 175 kilocycles andthe circuits are broadly side ofthe amplifier 9, the grid of the tube II being-connected to ground through a resistor I3. The grounded lead of the cathode of tube II includes the usual grid biasing resistor-shunt condenser network I4, and the anode of the tube is arranged for connection to a positive source of anode potential through the primary I 5 of the coupling transformer I6. nected in shunt with the primary coil I5 forfixedly tuning the output circuit of the amplifier I I to the intermediate frequency.

The secondary I8 of the transformer I6 is connected between the anode of the automatic volume control tube I9 and ground through ay path which includes the lead 20, the resistor 2I, the resistor 22, and the resistor 23. The lead 20 is additionally connected, through a resistor 24, to the low potential side of the input circuit of the amplifier 2. low potential sideY of the input circuit of the first detector 4 is connected, through a resistor 25 and lead 2B, to the junction of resistors 2I and 22, while the low potential side of the input circuit of the intermediate frequency amplifier 9 is connected throughv a resistor 21 and a lead 28 to the junction of resistorsr 22 and 23.

Direct current blocking condensers 29.are disposed in the cathode sides of the input circuitsy of the amplifier 2, the detector 4 and the amplifier 9, and a radio frequency by-pass condenser 30 is connected to ground from the junction of the resistors-24 and 2|.

The control tube I9 is shown as a triode, with its control grid strapped to the anode, the tube therefore functioning as a diode rectifier. The cathode of the tube I9 is grounded through a bias resistor 3l, the resistor 3l being shunted by a by-pass condenser 32. The transformer secondary IB is shunted by a condenser 33l which maintains the input circuit of the detector I9 fixedly tuned to the intermediate frequency. The symbol M5 denotes the fact that the resonant primaryand secondary circuits of transformer I6 are very closely coupled, and preferably sufliciently'overcoupled toresult in a resonance curve Characteristic of the type shown in Fig. 2.

ri`he automatic volume control network shown in Fig. 1, as stated heretofore, employs a twov element control tube and a special intermediate frequency amplifier to drive it. Y Due to its action the radio frequency voltage applied to the second detector I9 is substantially constant, for a signal of from microvolts input to that of several volts. Referring to the schematic circuit shown in Fig. 1 it will be noted that the volume control network functions in the following manner.V The input signal voltage for the intermediate frequency amplifier 9 is applied also to the control amplifier tube II' due to the grids of both amplifiers being coupled together by means ofthe condenser I2. y

rIhe output of the amplifier 9 is applied to the second detector through a partially tuned transformer. However, the output of the volumecontrol amplifier II is coupled to the control tube I9 through an overcoupled transformer circuit. The drop across resistors 2 I, 22 and 23'gives the control biasfor the radio frequency amplifier 2. The drop across resistors 22. and 23 comprises the control grid voltage for the first detector 4, and that across 23 provides the control grid voltage for the intermediate frequency amplifier 9.

As the drop in theseresistors is due to the signal voltage applied to the tube I9, and this voltage is in turn dependent upon the bias of the radio frequency amplifier, first detector and intermediate frequency amplifier, an automatic gain control action is obtained.

It will also be noted that the A condenser I'I is concondenser I5.

' The reason for the greater voltage applied to the radio frequency amplifier and the first detector than that applied to the intermediate frequency amplifier 9 is to prevent overloading of these tubes on the side of a strong carrier. The resistors 24, 25 and 21 function as filter resistors, and substantially suppress any ripples which may exist in the direct current potential. It will now be seen that as the tuning mechanism 8, which is to be understood as being associated with a tuning dial, is being adjusted to a desired signal carrier dial setting, such as WJZ for example, it is' extremely advantageous to have the relation between the receiver reproducer volume and the tuning dialadjustment comprise the curve shown in Fig. 3.

It will be observed from this latter curve that the greatest reproducer response occurs at the peak of the curve which is the signal carrier frequency, and that the reproducer response decreases sharply on either side of the carrier. Obviously, with this type of a relation the ear of the receiver operator can be readily employed to determine when the receiver tuning means is adjusted at the desired signal carrier. The relation 'shown in Fig. 3 cannot be secured without the employment of my present invention, and it will be noted that it can be secured in a simple and effective manner by merely overcoupling the primary and secondary circuits of the transformer I6 vsopas to impart to these two circuits a resonance curve of the type shown in Fig. 2.

An examination of this curve demonstrates that each peak of the curve is spaced five kilocycles fromvthe 1'75 kilocycle carrier, and that the depression of the curve occurs at the carrier frequency. With the transformer primary and seccndary circuits between the amplifier I I and control tube I9 possessing a characteristic of the type shown in Fig. 2, it is possible to secure the reproducer volume-tuning dial setting relation shown in Fig. 3. This follows in View of the requirement that the tube I9 holds its input substantially constant. Therefore, it KYautomatically varies the signal strength at the input to the amplifier 9 in a manner inverse to the ordinates of the curve of Fig. 2.

In order to secure the resonance characteristics shown in Fig. 2 it is necessary that the resistance in the primary and secondary circuits of transformer I6 be kept as low as possible. One particular method of minimizing the amount of resistance in the transformer I6 without changing the amount of inductance is to employ a core of magnetite around which the coils I5 and I6 are wound. It has been found that such a transformer construction has a minimum of resistance, and will facilitate the design of the coupling network between the tube II and the tube I9 so as to secure the resonance curve shown in Fig. 2.

-It is to be clearly understood that the coupling network between the amplifier II and the control tube IS shown in Fig. 1 is not the only method of securing the resonance curve of Fig. 2. For example, in Fig. 4 there is shown a modified coupling network wherein the strapped grid and anode of the tube I9 is coupled to the high potential side of the primary coil I5 by a coupling An absorption circuit comprising a coil I6 having a condenser 33' connected in shunt thereto, is coupled to the coil I5 in such a manner that the resonance curve shown in Fig. 2 is obtained. This type of circuit produces the desired resonance curve because the circuits I5,

I1 and I6', 33' are resonant to the same frequency. Those skilled in the'art will realize that the curve in Fig. 2 can be obtained in such a case.

In Fig. 5 there is shown still another modication to demonstrate that many types of coupling between tubes II and I9 are possible. In this modification the coil I5 has its high potential side coupled to the strapped grid and anode of tube lI9 by the coupling condenser I5. A path, including an inductance 50 connected in series with a condenser 5I, is connected in shunt with the coil I5, and a condenser 52 is connected in shunt with the path including inductance 50 and condenser 5I. This coupling arrangement functions to produce the resonance curve of Fig. 2. When circuit 50, 5I is made resonant to the desired operating frequency, the depression of the curve of Fig. 2 is obtained. The circuit including inductance I5 and condenser 52 is employed for fixing the off-resonance response of the curve.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is: Y y

1. In combination, with a radio receiver comprising a radio frequency amplifier, a detector having a tuned input circuit and a reproducer, a gain control tube coupled with the detector input circuit and the amplifier to maintain uniform the signal carrier level at the detector input circuit in spite of Variations in the signal carrier level impressed on the amplifier, and means including at least two overcoupled resonant circuits for coupling the gain control tube to the detector input circuit in such a manner that the coupling network has a double peaked resonance curve characteristic.

2. In combination, with a radio receiver `comprising a radio frequency amplifier, a detector and a reproducer, a gain control tube coupled with the detector input and the amplifier output to maintain uniform the carrier level at the detector in spite of variations in the signal carrier level impressed on the amplifier, means forcoupling the gain control tube to the detector input in such a manner that the coupling has a pronounced double peaked resonance curve characteristic, the coupling connection between said detector input and said gain control tube including an amplifier having its input coupled'to the radio frequency amplifier output and its output coupled to the gain control tube input.

3. In combination with a superheterodyne receiver including a radio frequency amplifier, a frequency changer circuit arranged to produce a desired intermediate frequency, an intermediate frequency amplier and a second detector, an automatic volume control network comprising an amplifier having its input coupled to a point between said frequency changer and said intermediate frequency amplifier, a gain control tube coupled to the output of said network amplifier, the gain control tube being connected to said radio frequency amplifier, frequency changer and intermediate frequency amplier for controlling the gain thereof to maintain the input to the second detector at a substantially constant energy level, the value of the coefficient of coupling between the amplier and the gain controlr tube of said volume control network being such that theresonance` curve of thel inputk of' thev gain control tube has a; double peak.A

4;. In combination with asuperheterodyne receiven including a radio,-` frequencyamplifier-g, a frequency. changer circuit arranged tov produce a; desiredY intermediate frequency., aninterme diate frequency amplifier and a secondi detector, an automaticvolume control networkcomprising.I an; amplifier havingA47 its-inputl coupled to apoint between' said frequency changer and saidintermediatey frequency amplifier a gain, control tube cqupled to. the outputofl said network` amplifier, the gain control tube being, connectedto.- said radiofrequency amplifienfrequency changer and intermediate frequency. amplifier` for controlling the. gain thereof to maintain the inputA to, the second detector atasubstantially constanten-,- ergy level, and means for, overcoupling theamf plifier and the. gain control, tube, of., said volume controlnetwork whereby theresonance curveof theI inputof the gain4 control tube hasfa., double peak.,Y Y

5;, In combination with a superheterodyne re.- ceiver, including aVA radio frequency amplifier,V a frequency changerA circuit arranged to producea desired intermediate frequency, anintermediate frequency amplifier and a, second detector,l an automatic volume control network,comprisingv an Yamplifier having its input coupledto a point.v between said frequency changer and said intermediate frequency amplifienagain controlr tube Ycoupled'to the` output. of saidl network amplifier,

thegain control tube being connected to said radio frequency amplifier, frequency changer and intermediate frequency amplifier for controlling the gain thereof to maintain the input to the second detector atea substantially constant` en-` ergy level, the value of the coefficient of coupling between the amplifier and thegain control tube of,k said volume control network being such that the resonance curve of the input of the gain con.- troltube has a double peak, said gain controltube being of the diode rectifier type and having its anode coupled tothe high potential, side of. the output of the volume control network amplifier.

6. A radio receiver comprisingahigh.frequency` amplifier having, aVV resonantv inputnetwork tuned to, a desired signal carrier frequency, Ya rectifier provided with a; cathode and at least one cold electrode, meansfor couplingsaid4 cold electrode to, said network, a direct.currentconnection, betweenl saidelectrode andfa gain control electrode of the amplifier, saidv couplingv means including, a, resonant network tunedr to said'.v frequency, ,the resonance curve characteristic` ofthe coupling means having a. pair offfrequencyA peaks each spaced from. said carrier frequency.`

7. A raclioreceiver comprising ahigh frequency amplifier having a resonant.V input network tuned, to a.,desiredfsignal. carrier frequency; a, rectifier( provided. withV a cathode and atleast one. cold electrode, Vmeans. for coupling saidy cold electrede to said network, a direct current. connec-v tion between saidA electrode and'. a gain control electrode of the amplifier, said coupling means including a resonant network tuned,- to said free. quency., the resonance curve vcharacteristic ofA the coupling means having a pair of frequency peaks each spaced -5 kilocycles fromY said carrierfref. quency.

8?. A radioreceivercomprising a high frequency amplifier having aY resonant input networktuned to a desired: signal carrier frequency, arectifierr provided with. a cathodeandat, least one cold;l

` electrode, means for. couplingA saidfcoldeelectrode.-

to the;L hihpotential side of.y saidnetworkJ; direct current; connection.Y between, said electrode` and al gainv control-r electrode of theamplifien, said couplinga means including a resonant network tuned tosaid frequency, the resonance curve characteristic'- of the Vcoupling meanshailing, af

pair of frequency peaks each spaced` fromt said,

carrier,` frequency.`

9; Ina radioV receiver of the type' including a` signal;` transmission; tube, a demodulator follow.- ing the-tube, a couplingnnetwork between thee-tube, and. demodulator, theV network havingv substanf` tiallly a.- single` peaked resonance;curvecharacteristie,l an automatic volumecontrol arrangement` forthe receiver comprising a. rectifierhaving-an;

output connection to said tube, a signal` couplingy network, comprising a transformerv having;` itsV primary and;s econdary. windings; overcoupled, be tween the rectifier and'theoutput ofV said tube, said. second network having a double; peaked resonance curve characteristic with a substantial. depression-between the peaks.

11. In a.` radio receiver of the; type including ai signal` transmission tube, a demodulator following theV tube, a coupling network between', the tube and demodulator the network having substantially4 a single peaked resonancev curve charjacteristic, an automatic volumeicontrol arrange-- mention the receiver comprising a, rectifierfha-wy ing an output connection to said tube, a, signal coupling network between the' rectifier and; the output ofsaid tubesaid second network having a; double peaked resonance curve` characteristic;

with a substantial depression between therpeaks,

the,` second network comprisingY a tuned Vcircuit coupled tothe rectifier, anda tuned.A absorptione .Y

circuit coupled solely to the tuned circuit.

12; Ina` radio receiver-of thetypeincluding a signal transmission tube, a` demodulator follow. ingA the tube, a.` coupling network between the, tubeand demodulator, the network having sub-v stantially asingle peaked resonance curve char-A acteristic, an` automaticvolume control arrangement for the receiver comprisingv a rectifier.- hav-` ing an output connection to saidftube,ja signaL coupling network between the rectifier andthe output of said tube, saidsecond network having a., double peaked resonance curve characteristicwith-v asubstantial depression between` the peaks; the second network comprising aseries resonant cir.A cuit,` and ananti-resonant'l circuit whose reactive' elements'are in shuntwith the seriescircuit.

13. In'l aradio receiver of the type including a. signal; transmission tube, a demodulator follow.- ingj the tube, a coupling network between the tube and demodulator, the network having-substantially/,fa single; peaked resonance curve characteristim. an; automatic volume cont-rol arrangement; for the receiver comprising; a rectifier hav-` ing. an; output connection, to said tube, awsignal coupling, network,y including atleast two. c oupled resonantV circuita. between.- the rectifierV4 andI theV output of said tube, said second network having a double peaked resonance curve characteristic with a substantial depression between the peaks, and said single peaked characteristic being substantially broad.

14. In a receiver which includes a signal amplier, a detector, and a reproducer following it, the detector having a tuned input network, an automatic volume control arrangement for the receiver including a diode rectier, the diode anode being connected to a gain control electrode of the amplier, and a signal coupling network between the diode electrodes and the tuned input network, the coupling network having a resonance Curve characteristic with a substantial depression at the received carrier frequency and a pair of spaced peaks at the extremities of the modulation side bands whereby the reproducer volume-tuning characteristic of the receiver has a peak at thel carrier.

CHARLES TRAVIS. 

